To obtain 3 mum lasers operating at room temperature, PbS single crystal growth, PbSrS/PbS DH and MQW lasers and HWE growth of PbCdSrS films lattice matched with the PbS substrate were studied. For single crystal growth of PbS, dependence of growth on substrate rod materials were mainly studied, Therod materials used for the growth were BaF_2 (111), SiO_2 glass, Al_2O_3(1000), and Al_2O_3(0101^^-). When SiO_2 glass and Al_2O_3 (0101) were used as the substrate rod, a large single crystal was obtained reproducibly. For PbSrS/Pbs DH laser, highest operating temperature was obtained at the active layer thickness of 0.5 mum. In the laser, lattice mismatch between PbSrS cladding layer and PbS active layer resulted in lattice strain of the PbS active layer. With increasing active layer thickness, the strain effect grad ually decreased and the lattice mismatch resulted in many misfit dislocations at the interface. For PbSrS/PbS MQW laser, increase of the operating temperature was not observed, but increase of the characteristic temperature, which shows a possibility to increase the operating temperature, was observed. PbCdSrS films lattice matched with PbS was also studied using the HWE growth technique, and good quality films were obtained.